SOM S Documen t I D 

# •niii i 200823 2

Explanatio n o f

Significan tDifference s Uppe r Californi a Gulc h Operabl e Uni t4 Californi a Gulc h Superfun d Sit e Leadville , C O

Marc h 200 4
U.S
. Environmenta l Protectio n Agenc y 99 9 18 * Street , Suit e 50 0 Denver , C O 8020 21 . Introductio n

Thi s Explanatio n o f

Significan t

Difference s (ESD ) describe s th e remova l o f planne d cleanu p work

fromth e constructio n schedul e for Fluvia l Tailin g Sit e 4 (als o know n a s Or o City ) withi n th e Operabl e Uni t 4 o f th e Californi aGulc h Superfun dSite
. Thi s chang e t o th e remed y defer s th e reevaluatio n o f th e nee dfor

clea n u p a t

Fluvia l Tailin g Sit e 4/Or o cit y unti l after th e revie w o f

sit e wid e surfac e an dgroundwate r post-constructio n monitorin g data
. Thi s ES D provide s informatio n abou t thi s chang e an dinclude s th e sit e history , selecte dremedy , basi s for th e change , support

agenc y comments , statutory determination s an ddocumentatio n o f publi c participatio n compliance
. Interes t i n th e cultura l an dhistorica l value s o f Fluvia l Tailin g Sit e 4/Or o Cit y ha s resulte d i n achang e t o th e selecte dremed y an dprovide s th e basi s for thi s ESD
. Alternative s for th e wor k planne dat

thi s are awer e initiall y discusse ddurin g ameetin g o n Ma y 4,1999
. Th e meetin g include dsupport staf f fromth e Colorad o Departmen t o f Publi c Healt h an d Environmen t

(CDPHE) , th e Stat e Historica l Societ y an dintereste dparties
. Th e U.S
. Environmenta l Protectio n Agenc y (EPA ) i s th e lea dfor thi s ESD
. A formal publi c commen t perio di s no t

require dfor

an ESD
. Comment s fromCDPH E ar e summarize di n Sectio n 5 o f thi s document
. EP A wil l publis h anotic e o f availabilit y an dabrie f descriptio n o f

th e ES D i n amajo r

newspape r

o f genera l circulatio n (a s require db y Cod e o f Federa l Regulatio n 40 , Sectio n 300.435(c)(2)(i)(B)
. Thi s ES D an dsupportin g document s wil l becom e apar t

o f th e Californi aGulc h Administrativ e Recor dfile an dinformatio n repository [a s require db y CF R40 , Sectio n 300.435(c)(2)(i)(A ) an d300.825(a)(2)]
. Comprehensiv e informatio n o n th e Californi aGulc h Superftin dsit e i s availabl e at : U.S
. Environmenta l Protectio n Agenc y Regio n VII I Superfun dRecor dCente r 99 9 18*Sfreet , 5*^Floor Denver , C O 8020 2 (303)312-647 3 an d Lak e Count y Publi c Librar y 111 5 Harriso n Avenu e Leadville , C O 8046 1 (719)486-056 9 O n Marc h 31,199 8 th e Recor do f Decisio n (ROD ) for

th e Uppe r

Californi aGulch , Operabl e Uni t

4 , was signed
. An y significant , but no n fimdamental, change s t o th e selecte d remed y mus t

b e publicl y notice dunde r Sectio n 11 7 o f

th e Comprehensiv e Environmenta l Respons e Compensatio n an dLiabilit y Ac t o f 198 0 (CERCLA) , a s amende db y th e Superfun d Amendmen t

an dReauthorizatio n Ac t o f 198 6 (SARA) , an dpursuan t t o CF R40 , Sectio n 300.43 5 (c)(2)(i) , 5 5 Federa l Registe r 8666 , 885 2 (Marc h 8,1990)
.

### 2 . Sit e Histor y an d Contamination Th e Californi aGulch Superfun dSit e i s located10

0 mile s southwes t

o f Denve r i n Lak e County , Colorado
. The Sit e cover s 1 6 '/

amile s an dinclude s the Cit

y of Leadville , variou s part s of th e Leadvill e Histori c Mining Distric t andStringtown
. A section of th e Arkansa s Rive

r from th e confluenc e o f

Californi aGulc

h to the confluenc e o f

Lak e For k Cree k i s als o included
. Th

e Sit e wa s place do n th e Nationa l Prioritie s Lis t

du e to concern s abou

t th e impac t

of min e drainag e on surfac e water s in Californi aGulch an dth e impact

o f heavy metal s loading i

n th e Arkansa s River
. The 199 4 Consen t Decre e dividedth e Sit

e int o th e 1 2 Operable Unit s (OUs ) show n in Figur e 1
. OU s 2 throug h 1 1 wer e designate dto facilitat

e sourc e remediatio n andcorrespond wit h area s of responsibility
. O

U 12 , which cover s th e entir e Site , wa s designate dto addres s Site-wide Surfac e an

dGroundwater
. O

U 1 2 will b e addressedafte r completio n of

sourc e remediatio n in O

U 2 throug h 11
. Uppe r Californi aGulch , O

U 4 , i s avalley wit

h a n intermitten

t sfrea mtha t flows to th e confluenc e wit

h th e Arkansa s River
. Th

e subject of thi s ES D i s Fluvia

l Tailin g Sit

e 4/Or o City , which i s asub-basin of

Uppe r Californi aGulch , O

U 4
. Resurrectio n Minin g Compan y i s responsibl e fo

r conductin g all respons e action s a t O U 4
. Th e genera l locatio n of

th e sub-bas m i s shown on Figur

e 2
. Primar y contaminan

t sourc e area s wdthi

n Fluvia l Tailing Sit

e 4/Or o Cit y include seve

n wast e rock pile s an dFluvia l Tailin g Sit

e 4
. Wast e roc k surfac e sample s sho w elevated concentration s o f

cadmiu man dlead
. Fluvia

l Tailin g Sit

e 4 contain s a

n estimate d102,000 cubi c yard s o f

tailin g (intermixe dv^dt

h alluvia l sediments ) an

dextend s fo

r 1. 5 mile s along Uppe r Californi aGulch
. Fluvia

l Tailin g Sit

e 4 sample s show elevatedconcentration s fo r arsenic , cadmium , copper , lea dan dzinc
. Sinc e residential , commercia l an dindustria l use s d o not occu r i n O U 4 , recreationa

l visitor s wer

e selecte da s th e focu s of

th e Ris k Assessment
. Result s o f thi s stud y indicate dtha

t risks to visitor s fromexposur e to contaminant s in wast

e roc k andsurfac e tailin g di dnot

exceedEP

A level s o f

concern . EPA' s 5-Yea

r Review o f

th e Californi aGulch Sit

e concludedtha

t ther e i s acontinue d presenc e o

f meta l an datypica l p H contaminatio n withi n the Uppe r Californi aGulc

h surfac e wate r despit e completio n of

mos t of th e respons e actions
. Remedia l actio n a t Or o Cit y ma y ultimately b e necessary . EP A will continu e monitorin g the site
. Stor meven t datacollecte dby EP

A fo r astor mtha t occurredi n July 200 3 indicateda

n 84 % increas e i n zinc loading in Californi aGulch between sample location s up an ddownstrea

mo f Or o City
. EP

A will continu e to collec t

stor meven t datat o bette r understan dactua

l impact s t o th e environment
. Sedimen t sampling conductedb y EP A in Augus t

of 200 1 indicate dtha

t sediment s a

t Or o Cit y exceede d(EPA) ECOTO X threshol dvalue s fo

r all metal s except

manganes e an

darseni c (an dzin c i n on e instance ) thu s indicatin g tha t th e erosio n of

thes e sediment s durin g stor m event s coul dadversel

y impac t wate r qualit y in Californi aGulch
. The erosio n an dsubsequen

tdepositio n o f thes e meta l lade n sediment s ma y als o serv e t o re-contaminat e dow n strea m reache s o f

th e gulc h tha t

hav e alread y bee n remediated
. EP A wil l continu e t o monito r sedimen t erosion , resultin g fromstor mevent s an dannua l sprin g runoff , t o determin e thei r

actua l impact s o n th e environment
. 3 . Selecte d Remed y Th e RO D for

Uppe r Californi aGulc h presente dth e selecte dremed y for th e sub-basi n Fluvia l Tailin g Sit e 4/Or o City
. Th e selecte dremed y for thi s sub-basi n involve dreconstructin g th e Uppe r Californi aGulc h streamchannel , regradin g th e channe l spoi l materia l an dregradin g selecte dfluvial tailin g areas . Specifi c element s included :

Channelizatio n o f

approximatel y 8,60 0 feet o f Uppe r Californi aGulc h Regradin g an dblendin g o f channelizatio n spoi l materia l int o adjacen t area s Regradin g o f

sid e slope s alon g channe l Mino r surfac e regradin g t o enhanc e positiv e runof f Amendin g an drevegetatin g approximatel y 1 6 acre s Constructio n o f

approximatel y eigh t

sedimen t dam s Constructio n o f

approximatel y 1. 5 acre s o f wetlands Th e RO D di dno t

identif y wate r qualit y goal s fo r

surfac e streams an dheav y meta l contamination
. Therefore , EP A agree dt o establis h surfac e an dgroundwate r requirement s whe n EP A an dCDPH E hav e determine dallowabl e wate r quality standard s unde r

O U 12
. Thi s i s pursuan t

t o th e 199 4 Consen t

Decree , whic h designate d0U1 2 t o addres s Site-wid e surfac e an dgroundwater
. I n addition , th e Consent Decre e state s tha t

O U 1 2 wi

U b e addresse donl y afte r completio n o f

sourc e remediatio n i n OU s 2 throug h 11
. Th e Consen t Decre e als o recognize dtha t

additional sourc e remediatio n o f othe r appropriat e respons e action s relate dt o surfac e o r groundwate r

coul doccu r

a s par t o f O U 1 2 anywher e withi n th e Site
. 4 . Basi s fo r an d Descriptio n o f Significan tDifference s Du e t o th e presenc e o f

historica l propertie s withi n O U 4 , th e RO D specifie dtha t remedia l desig n occu r

i n consultatio n with th e Stat e Histori c Preservatio n Officer
. Historica l site s identifie da s eligibl e for

listin g o n th e Nationa l Registe r o f Histori c Places ar e identifie da s contributin g t o th e Leadvill e Histori c District
. Thes e ar e th e subjec t o f th e Cultura l Resourc e Inventory o f

Selec t Min e Wast

e Roc k Pile s an dFluvia l Tailin g Location s in Operabl e Uni t 4 o f th e Californi aGulc h CERCL A Site , Lak e County , Colorado
. Fluvia l Tailin g Sit e 4/Or o City i s identifie da s acontributin g elemen t o f th e histori c Leadvill e Minin g District
. Durin g th e remedia l desig n process , ademonstrate dinteres t i n th e cultura l an dhistorica l value s o f Fluvia l Tailin g Sit e 4/Or o Cit y wa s expressed
. Thi s informatio n triggere dth e consideratio n o f altemative s t o th e selecte dremed y an dprovide s th e basi s for thi s ESD
. I n 1998 , Colorad o Preservatio n Inc
. (CPI ) place dth e Leadvill e Minin g Distric t o n it s lis t o f "mos t endangered " places
. CPI' s 199 8 site tour , an dth e opinion s expresse db y loca l an dstat e governmen t representative s wh o too k part i n th e tour , wer e instrumenta l i n EPA' s decisio n t o defer clean-u p work

a t Or o City
. Altemative s for

th e wor k planne dat

Or o City wer e discusse ddurin g ameetin g o n May 4,1999
. Th emeetin g include dCDPHE , representative s o f th e Advisor y Counci l o n Histori c Preservation , th e Stat e Historica l Societ y an dintereste dparties
. Intereste dpartie s recommende dvariou s alternativ e method s t o addres s contaminatio n i n th e Or o City area . I n respons e t o th e cultura l an dhistorica l value s expresse di n that meeting , EP A ha s remove dth e clea n u p wor

k planne dfo r

Fluvia l Tailin g Sit e 4/Or o City fromth e constructio n schedul e for O U 4
. Therefore , thi s sub-basi n i s no t subjec t t o an y remediatio n at

thi s time
. Th e nee dfo

r clea n u p i n th e are awil l b e reevaluate dafte r reviewin g Site-wid e surfac e an dgroundwate r post-constructio n monitorin g data
. Th e Consen t Decre e recognize s tha t

additiona l sourc e remediatio n o r othe r appropriat e respons e action s relate dt o surfac e o r groundwater

coul doccu r

a s part o f O U 1 2 anywher e withi n th e Site
. Consequently , thi s ES D doe s not alte r th e possibilit y fo

r future respons e action s withi n Fluvia l Tailing s Sit e 4/Or o City
.

Include di n thi s ES D determinatio n ar e curren t groundwate r

an dsurfac e wate r analyse s fromth e site
. A recen t assessment , date dJun e 11* , 2002 , summarize s th e surfac e wate r meta l concentration s an dload s i n th e histori c Or o City area . Overall , flows, concentratio n an dcalculate dload s o f th e ke y meta l parameter s (excep t dissolve dlead ) decreas e i n Uppe r Californi aGulc h acros s th e entir e reac h o f th e Or o City area . Specifi c trend s o f

th e ke y parameter s includ e th e decreas e o f arsenic , cadmium , coppe r an dmanganes e concentration s acros s th e Printe r Bo y fluvial tailing s are adurin g bot h baseflo w an dhig h flow. Durin g baseflow , ther e i s a n increas e i n iron , sulfat e an dzin c concenfrations , however , th e concentration s decreas e acros s th e segmen t durin g hig h flow. I n addition , thoug h ther e i s a n increas e o f th e meta l load , i t

i s relativel y mino r

an daccount s for les s tha n 1 0 percen t

o f th e meta l loa dacros s th e entir e area . I n respons e t o th e informatio n containe di n th e wate r qualit y assessment , n o further remediatio n wil l tak e plac e i n OU4/Or o City at thi s time
. With thi s informatio n an dth e informatio n fromth e cultura l an dhistori c preservatio n meeting , n o actio n wil l b e take n i n th e OU4/Or o City area . Furthe r sourc e remediatio n may b e require dunde r O U 12 , whic h cover s th e entir e sit e surfac e an dgroimdwater
. O U 1 2 wal l b e addresse dafter

sourc e remediatio n i s complete di n O U 2 throug h 11
. 5 . Suppor tAgenc y Comment s Th e Colorad o Departmen t o f Publi c Health an dEnvironmen t (CDPHE ) support s EPA' s decisio n t o defer remedia l actio n a t

th e Or o Cit

y site , unde r

th e O U 4 Recor do f

Decision , whil e th e agencie s gathe r additiona l wate r

qualit y dat at o determin e whethe r remediatio n o f

th e Or o Cit

y site i s necessar y t o protec t

huma n health an dth e environment
. However , CDPH E believe s tha t som e sort

o f remed y ma y ultimatel y b e necessar y t o addres s contaminatio n emanatin g fro mth e Or o Cit y site
. 6 . Statutor y Determination s Unde r CERCL A Sectio n 121 , EP A mus t selec t aremed y tha t

i s protectiv e o f

huma n health an dth e environmen t tha t complie s wit h ARAR' s an di s cos t effective
. EP A believe s tha t th e ne w alternativ e t o th e RO D for Fluvia l Tailin g Sit e 4/Or o City i s appropriat e an dth e remed ywil l remai n protectiv e o f huma n healt h an dth e environment
. Th e selecte dremed y wil l continu e t o compl y wit h federal an dstat e requirement s tha t ar e applicabl e an drelevan t an dappropriat e t o th e remedia l action
. Thi s ES D doe s not fundamentall y chang e th e remed y an di s cos t effective
. Sectio n 12 1 als o state s tha t EP A mus t

selec t aremed y tha t

use s permanen t

solutions , alternativ e treatmen t

technologies , o r

resourc e recover y technologie s t o th e maximu mexten t practicable
. I n addition , CERCL A prefer s remedie s tha t includ e treatmen t

tha t permanentl y an d significantl y reduce s th e volume , toxicity , o r mobility o f

hazardou s waste s a s aprincipa l elemen t o f th e remedy
. I n th e Fina l Focuse dFeasibilit y Study , i t wa s determine dtha t

treatmen t o f th e Uppe r Californi aGulc h wast e roc k an dfluvial tailin g materia l wa s impracticable
. 7 . Publi c Participatio n Complianc e EP A wil l publis h anotic e i n th e Heral dDemocrat newspape r

tha t describe s th e ES D an d it s availabilit y for

revie w (unde r

Sectio n 117(c ) o f

CERCLA , 4 2 U.S.C
. Sectio n 9617)
. A forma l publi c commen t

perio di s not

require dwhe n issuin g a

n ESD
. Thi s ES D an dal l document s tha t suppor t th e change s an dclarification s ar e containe di n th e Administrativ e Recor do f th e Californi aGulc h Superftin dSit e (unde r CF R40 , Sectio n 300.435(c)(2)(i))
.

Date dMaxjLDodso n ' Assistan t Regiona l Administrato r U S EP A Regio n 8